NEW YORK (Reuters Health) -- Laser-based vision correction, such as LASIK, usually results in greatly improved visual acuity, but occasionally it can be followed by a clouding in the center of the cornea and poorer vision.

Fortunately, the corneal opacification resolves on its own within a matter of months, according to two ophthalmologists in Los Angeles, and the related vision problem is safely reversed with a repeat laser treatment.

Dr. Baris Sonmez from the David Geffen School of Medicine at UCLA and Dr. Robert K. Maloney from the Maloney Vision Institute describe their experience with what they term "central toxic keratopathy" following laser refractive surgery in the American Journal of Ophthalmology.

The eye specialists note that such cases have been reported since 1998. To better characterize the condition, Sonmez and Maloney reviewed the charts and clinical photographs of 14 affected patients they had treated.

Altogether, 23 eyes were involved; in 19, the condition arose after LASIK treatment (an acronym for laser in situ keratomileusis), and 4 cases occurred after a similar procedure, PRK or photorefractive keratotomy.

Opacification of the cornea usually began within 3 to 6 days after the procedure. It occurred only in the very center of the cornea, where the highest laser energy is directed during the treatment. The affected eyes also became 'hyperopic', meaning that the focus was abnormal.

The opacification cleared over a period of 2 to 18 months.

Sonmez and Maloney say that central toxic keratopathy is not an inflammation, and warn that corticosteroids should not be used to treat it because long-term use until the cornea clears would raise the raise the risk of glaucoma, cataracts, and vision loss.

Seven patients underwent successful LASIK enhancement after their corneas cleared. The fact that corneal problems did not recur after repeat LASIK suggests that "some external inciting factor is necessary" for the condition to develop. Sonmez and Maloney hypothesize that it is "a toxic reaction to some substance that undergoes photoactivation by the laser."